Optical system to form highly compressed bright line image of light source



H H H ooooogowu lilw ll A. J. HOLMAN OPTICAL SYSTEM TO FORM HIGHLY COMPRESSED BRIGHT LINE'IMAGE] OF LIGHT sou Filed April 2, 1952 April 7, 1936.

April 9 A J. HOLMAN 2,036,275

OPTICAL S YSTEMTO FORM HIGHLY COMPRESSED BRIGHT LINE IMAGE OF LIGHT SOURCE Filed April 2, 1932 2 Sheets-Sheet 2 [liven/0r Z In Patented Apr. 7, 1936 UNITED STATES 2.038.275 I or'rrosr. srs'rnlu ro roam menu cou- PRESSED BRIGHT SOURCE LINE IMAGE OF LIGHT Arthur J. Holman, East Orange, N. .1. Application April 2, 1932, Serial No. 602.668

12 Claims.

My invention relates to an optical system adapted to produce a liner and brighter light line for use in recording and duplicating photographic sound records, and in the reproduction of sound from such photographic sound records. Bound motion pictures are decidedly inferior in tone quality particularly in the reproduction of music and the female voice. Although it is possible, by careful application of laboratory methods, to

record with considerablefldelity sounds having irequencies up to 10.000 cycles and even higher, there is no sound equipment available at the present time which is capable of reproducing such high frequencies, even from the original sound recordings. Moreover, sound motion pictures suffer much from the further degrading of tone quality caused by inferior duplication, on'the" positive prints, of the original high.frequency' recordings. As a consequence, the timbre and color of musical selections when rendered in sound pictures, are so obviously inferior that the great majority of musical comedy motion pictures have been financial failures. The loss of the higher overtones from the reproduced human voice removes ti very characteristics by means of which we are enabled to distinguish one voice from another, so it is not surprising that, at sound motion picture exhibitions, the voices of actresses are always reproduced in toolow a key and are scarcely distinguishable one from another.

The upper limit of the sound frequency range, 1. e. the highest pitch note, which can be recorded in a photographic sound record is dependent chiefly on three factors, namely, the linear velocity of the film across the recording aperture, the height (measured in the direction of motion of the film) of the recording light line, and the resolving power of the photographic emulsion wherein the sound is recorded. Experience has .19 proven that the resolving power of the photographic emulsion, i. e. the size of the silver haloid grain, is not the limiting factor in determining the maximum sound frequency which can be successfully recorded at the established film velocity of 45 24 frames (approximately 18 inches) per second. With film velocity standardized at 24 frames per second for standard millimeter film, there remains only one means of improving the quality of commercial motion picture sound recording, 50 name-y by reduction in the effective height of the sound track recording line.

The fidelity with which sounds, particularly those of high irequency, can be reproduced from a sound record is determined first, by the height as of the scanning line, and second, by the combined characteristics of the amplifying system and the loud speakers. Electrical amplification has been steadily improved and loud speakers are available for reproducing bound frequencies far beyond the working range'used commercially in sound motion 5 pictures. so here againmuch improvement in sound quality can be expected from the use 01 a finer and intrinsically brighter scanning line. Considerable theory has been developed in connection with ideal recording and reproducing 10 which pre-supposes a recording and scanning line of infinitesimal height, and some approximations have been made as to the rate of falling ofi'in efilciency of reproduction, particularly of the high pitch notes, the height of the scanning line is is increased to the values which usually obtain in commercial practice. From this data it appears that a reduction of only 50% in the height of the scanning line will increase the efilciency of reproduction, by several hundred per cent, of those 20 higher overtones the absence of which is the unmistakable characteristic of "canned music."

Present practice in constructing exciter systems calls for a mechanical slit having height to width ratio equal to the proportions of correg spending dimensions of the scanning line. This proportionality between the slit and the scanning line obtains because the scaning-line, which is a reduced image of the mechanical slit, is formed on the film by a high grade well correct- 10 ed microscope obiective. The mechanical slit is illuminated by a coil filament incandescent lamp and usually a condenser is interposed between the filament and the slit joincre'ase" the illumination on the slit. To make the system reasonas ably easy to adjust and to eliminate the detai mental efi'ect of a sa ing filament, the light band formed at the slit by the condenser is many times the height 0! the slit itself, hence the systemis exceedingly ineiilcient as a light transmitter. It has been found impractical to make the slit much over one half inch in width, hence, tor the usual length of scanning line, the optical reduction from slit to image cannot'exceed- 4 or 5 to 1, so theoretically, ii the scanning line is to be .001 g inch in height, the height of the mechanical slit will be .004 or .005 inch. A certain amount of aberration is associated with lilht passing an edge regardless of the type of optical system beingused,andwhenanarrowslitisformedbe-go tween two edges the multiplied aberration "resulting therefrom is very detrimenta. to the definition of the image Droiected on the sound track by the objective. While the theoretical heightof the scanning line may be .001 inch, the actual ":FT, o' iiriin ber-renown,

rection. ffhile; cylindriced condcnser ieiement: msy increase ssneterieliykthe spot' "efiicient:yr.e.t

the slit, it is doubtful ii the increased light can be so directed through the slit as to increase the brightness of the image formedbythe Inlcro: scope objective. Moreover thefproblemoif'edge aberration at the slit is not solved by'the use of is cylindrical condenser element.

My invention includes the use oi's sphero-cyllndricel objective system for forming 0, highly compressed line image of o suitoble light source. Such objective eliminates the necessity for mcchsnlcel slit because sphero-cylindricsl elements bi-ic-csi in the sense that their refractingpower is different in planes st right'sn zles, hence the image of an incandescent lamp file.- ment may be reduced many times more in diameter than in length. With the mechanical slit eliminated the aberration problem is much sirnplified. I have learned from years of experience with precision cylindrical lenses that the aberrations therein are relatively less than for sphericrd lenses, therefore a sphero-cyllndricel objective tern ofiers the further advantage over the micro one objective, of improved correction.

improved exciter optical system may be best understood by reference to the accompanying dropinse in which Fist. 1 plan view showing relative positions of 672C .er objective, film end photo-electric cell in en migrcment wherein the light been through an engie of 90 degrees within the object e Flo. '2 is elevation of the arrangement shown in Fist. 1. shoving relative position oi the sound track.

3 is plan View showing exciter lump, sphero-cylindricul condenser, objective, him and also on end view of the objective.

Fig. is in elevation of the parts shown in 8. showing relative position 01' the sound track.

Fig. 6 is top and end view of the sphero-cyiindrlcril objective showing the cylinder achromotircd.

Fist. 8 is plan View showing relctive positions or exciter lcmp, objective, film and photo-electric cell, and end view of the objective, in an or rengzcrnent wherein the axis of the light beer: is turned through on ingle in the objective.

7 it elevation oi the parts shown in Flo.

shows another form of the objective iliustr mperes, having a coil .022 inch in diameter and w coror-firnntely '3 inch long mrjc of wire .096 inch in diameter, is suitable for our purpose. The objective 5-, having spherical surface 9 and o cylindrical surface *3 (Fig. 3) is suitably mountcd in front of the film strip 1, with the eris of symmetry oi its spherical surface parallel to frame lines on the film and in line with the midpoint of the coil filament the axis of coil filement 2 being at right angles to said earls of symmetry. An optically flat surface 8, on' ective meking an angle of ib degrees to the eras of sym metry oi the spherical surface provides an. internal reflecting surface which redirects light from the exciter lamp through the cylindrical surface ii, to the film l, where e sharp image oi the filament 8, is formed on the sound track 8, by the combined refrecting powers of the spherical surface 5, and the cylindrical surface t.

Wherever the sound track is transparent or translucent, under the filament imege, light from the exciter lemp l, is transmitted through the film i into the photo-electric cell it, which is suitably supported behind the film in such position that the light transmitted by the film falls centrally on the semi-circular shield ii, forming the cathode of the photo-electric cell The him i, is moved at uniform velocity past the scanning line, and means must be provided for so moving the film and for accurately meinteining the distance from the objective to the film i for the entire sound pick-up mechanism are I omitted from the specification end drawings The axis of filament 8 lies in the plane normal to the edge of the film strip eat the sound pick-up position, hence the compressed image of the filement formed on the film 'i over the sound track ll, will be exoctly at right angles to the direction of motion of the film. Provision must be made also for adjusting the exciter lamp along the axis o1 the objective for the purpose of iocusing.

To secure a. brighter image of the filsment st the sound track 9, e sphero-cylindrical condenser iE, (Figs. 3 and 4) having is sphericel surface l3, and s cylindrical surface i i, is interposed between the exciter lump end the olojective in close proximity to the exciter lamp. The con denser i2, is so oriented that the suds of the cylindricsl surface id, is parallel to the sods of the coil filament 3. The retracting power of the spherical surface it, is just sufilcient to'bend the marginal rays from the end of the fllsunent so they will be directed into the objective i es shown in Fig. 3. Since the axis of the cylindrical surface i i, is perollel to the axis of the coil filsment 5%, it is to be observed that the cylindrical surface has no retracting power in the plane shown in Fig. 3, hence the rays in this plane ere unnffected by the cylindrical surface, but in the plane st right angles thereto, illustrated in Fig. 4, the retracting powers of the spherical surface i i,

end the cylindrical surface i i, are cumulstive,

hence is greeter wedge angle of light may be col lected and so directed into the objective that it will add to the brilliance of the imege formed on the sound track by the objective ii. The condenser l2, is placed close to the enciter lamp i,

first, to collect and parallel the greatest solid angle of light, and second, to cause a minimum magnification oi the filament as viewed from the position of the objective.

The objective '1, (Fig. 3) is so designed that.

film surface. The two fundamental laws of lenses, which determine the relative sizes of object and image and the relative distances thereof in terms of the focal length, are fully complied with in the objective. It is to be observed that the equivalent center of the objective for the plane illustrated in Fig. l, is on the axis at the spherical surface. The objective is so designed that the length of the scanning line is to the length of the filament as the mean distance from the spherical surface to the image (corrected for part glass and part air path) is to the distance from the filament to the spherical surface, when the image distance and object distance are correctly adjusted for sharp focus. In the plane at right angles to the axis of the cylindrical surface, the equivalent center of the objective lies within the objective but relatively close to the cylindrical surface, and, since the ratio of fllament width to scanning line height is equal to the ratio of the respective distances of object and image from this equivalent center, it is obvious that a high reduction ratio can be obtained easily without departing from the distance relations required for the reduction in image length hereinabove specifled. Thus the problem resolves itself into the determination of the required relationship of the two equivalent centers, each to the other, and also to the filament and the sound track at the scanning position. Having once recognized'the advantages of the sphero-cylindrical combination, it is an easy matter for anyone skilled in the art of lens design to lay out an objective having the required relative refracting powers in sphere and cylinder and the correct spacing to fulflll the conditions herein specified.

The use of a sphero-cylindrical condenser lens as shown in Figs. 3 and 4, will increase the amount of light which may be added to the scanning line, and, if the condenser lens is well made and positioned close to the exciter lamp, the deflnition of the image will not be impaired. Whenever a very bright line is required and extreme fineness is not desirable or advantageous, the use of a condenser is recommended, but when an extremely fine scanning line is desired it is probably advantageous to use the sphere-cylindrical,

objective without the condenser.

While I have described and illustrated various forms of my improved sphero-cylindrical objective, some of which are achromatized, it is to be understood that other combinations of spherical and cylindrical surfaces may be used for the purposes specified, i. e. the projection of a compressed line image of an incandescent filament, or other light source, ona photographic sound track or on a photographic emulsion for sound recording purposes. It is also to be understood that the optical axis may be redirected differently within the objective, or exterior thereto. as mechanical parts of the film feeding apparatus may require. The appended claims are intended to cover any and all combinations of spherical and cylindrical refracting surfaces whenever such combination functions as and for the purpose specified.

Although I have described my improved sphere-cylindrical objective as related to sound motion pictures and more particularly to a sound pick-up system for reproducing sound in connectionwith motion pictures, it is to be understood that my device is useful wherever a flne bright light line may be required for any purpose, hence the appended claims are to be interpreted as covering my invention in whatsoever connection it may be used. My device may be applied to advantage in connection with the photographic recording of sound, and it should also prove useful in the duplicating of the original sound recordings on the positive prints used for projection.

It is obvious that a toric surface might be substituted for the spherical and, or for the cylindrical surface on the objective and condenser illustrated in the drawings, and an objective and condenser thus made would be quite an improvement over the microscope objective and optical system now being used for producing the scanning line. There is a decided advantage, however, in using a cylindrical element in close proximity to the film position because it offers the only means of obtaining the maximum reduction in image height. Interchangeability of toric and spherocylindrical lenses is recognized by those skilled in optics, hence it is to be understood that the appended claims are drawn broad enough to include these and any other combination of refracting surfaces capable of functioning in the manner and for the purposes specifled.

Having thus fully described my invention, what I claim is 1. In a photo-electric cell .exciter system, a single element bi-focal objective having a spherical refracting surface and a cylindrical refracting surface, said cylindrical surface having several times the refracting power of said spherical surface and being positioned adjacent the image plane, said refracting surfaces being spaced to provide common conjugate planes for both focal lengths of said bi-focal objective.

2. In a photo-electric cell exciter system, a single element bi-focal objective having a spherical refracting surface, a cylindrical refracting surface and a reflecting surface, said cylindrical surface having several times the refracting power of said spherical surface and being positioned adjacent the image plane, said refracting surfaces and said reflecting surface being spaced and arranged to provide common conjugate planes at right angles for both focal lengths of said bi-focal objective.

3. An achromatized bi-focal objective comprisinga flint glass element having a convex spherical refracting surface and 'a concave cylindrical refracting surface, and a crown glass element cemented to said flint glass element, said crown glass element having twoconvex cylindrical refracting surfaces one of which is suitably formed to fit into the concave cylindrical surface on said flint element.

4. An achroma'tized bi-focal objective comprising a flint glass element having a convex spherical refracting surface, a concave cylindrical refracting surface and a flat reflecting surface 0pposite said refracting surfaces, the axis of the cylinder forming said concave cylindrical re-' fracting surface being parallel to the axis of.symmetry of said spherical refracting surface and forming an angle of 45 degrees with said reflecting surface, and a crown glass element cemented to said flint. glass element, said crown glass element having two convex cylindrical refracting surfaces the axes of which are parallel, the refracting power of each of said cylindrical surfaces belng greater in one plane than that of said spherical surface.

5. A bi-focal objective with maximum and minimum ref acting power in planes at right angles, said -0 jective having such rectangular contour as to provide approximately equal effecspacers 5 tive apertures (t" values) in each of said planes.

8. An achromatic bi-tocal objective comprising an achromatic element having spherical retracting surtaces and an achromatic element having cylindrical retracting surfaces, said elements being curved and spaced to provide a pair 0t con jugate object and image planes common to both local lengths ot said bi-tocal objective, substantially as and tor the purpose specified.

7. In an optical system ot the character specified. the combination ot a single element bi-tocal condenser and a single element bi-tocal objective, the planes ot maximum and minimum retraction ot said condenser and said objective being common to both, said planes intersecting at right angles along the axis ot said optical system.

8. In an optical system ct the character specified, the combination of a sphero-cylindrical condenser and a sphero-cylindrical objective each comprising a single element, said condenser and said objective being positioned on a common optical axis and being so oriented'that the axes of the cylinders torming the cylindrical surtaces lie in a common plane.

9. In an optical system 0! the character specified, the combination of a light source presenting a narrow rectangular light area, a bi-tocal ob- Jective having but two glass-air retracting surtaces and being positioned with its plane of greater retracting power parallel to the short sides at said rectangular light area, and a film strip carrying a photographic sound track, said film strip being adapted and arranged to cross the axis ot said optical system at right angles, and said rectangular light area and said sound track lying in conjugate planes common to both tocal lengths at said bi-tocal objective.

10. In an optical system at thecharacter specified, the combination ot a light source presenting a narrowrectangular light area, a bi-tocal spheroc'ylindrlcal single element objective positioned with its plane of greater retracting power parallel to the short sides or said rectangular light area, said bi-tocal objective being arranged to turn the optical axis through an angle at 90 degrees, and a film strip carrying a photographic sound track, said film strip being adapted and arranged to cross the axis 0! said optical system at right angles, and said rectangular light area and said sound track lying in conjugate planes common to both tocal lengths ot said bi-tocal objective.

11. In an optical system ot the character specified, the combination 0! a light source presenting a narrow rectangular light area. a bi-tocal condenser posltioned close to said light source and oriented so that its plane ot greater retracting power is parallel to the short aides oi said rectangular light area, a bi-tocal objective positioned with its plane ot greater retracting power coincident with said first mentioned plane, and a film strip carrying a photographic sound track, the relative spacing ot said parts and the retracting powers at said bi-tocal objective being such that said rectangular light area and said sound track lie in conjugate-planes common to both focal lengths at said bi-tocal objective.

12. In an optical system ot the character specified, the combination ot a bi-tocal objective having but twoglass-air retracting surfaces spaced to provide common conjugate planes tor both tocal lengths, a narrow rectangular light source, and a film strip carrying a photographic sound record, said objective being placed with its surface 0! highest retracting power in close proximity to said film strip. said parts being positioned and oriented with respect to said objective to produce a highly concentrated,'sharply defined, bright line image of said light source in the plane ot said sound track and at right angles to the edges thereot.

. ARTHUR J. HOLMAN. 

